Protective coating for concrete pavements



May 9, 1944.

G. H. SANDENBURGH PROTECTIVE COATING FOR CONCRETE PAVEMENTS ,F'iled March 13, 1940 Patented May 9, 1944 7 PROTECTIVE COATING FOR CONCRETE PAVEMENTS George H. 'Sandenburgh, Ann Arbor, Mich., as-

signor of one-half to William M. Pindell, Evans ton, 111.

Application March 13, 1940, Serial No. 323,647

6 Claims. (01. 94-23) This invention relates to improvements in protective coatings for concrete pavements and it consists of the matters hereinafter described and more particularly pointed out in the appended claims.

It is known that a concrete pavement is porous and will absorb moisture. In severe weather the absorbed moisture freezes and expands and in expanding exerts a great pressure that causes the concrete to spall, crack or chip. As the weather abates, the pavement thaws out and this alternate freezing and thawing is one of the causes of the disintegration of a concrete pavement.

In some communities where snow and freezing weather is present, it is the custom to apply a grit, such as sand or cinders, to the icy pavement so that better traction and safer driving conditions are possible. To prevent such grit from 118- ing whipped off the surface of the pavement by rapidly moving traffic, the pavement is often treated with a material such as calcium chloride or sodium chloride. Either of these materials will go into solution and melt the snow and ice on a pavement, and carry the grit into the snow or ice so as to be trapped therein and provide i pervious to moisture but prevents the penetration of thawing and melting solutions into the pores of the concrete so that disintegration of the concrete pavement due to such penetration, is either reduced to a minimum or is entirely prevented.

Another object of the invention is to provide a protective coating for a concrete pavement which not only provides a good traction surface, but which will not creep, dry out, check or crack. A further object of the invention is to provide a protective coating for the purpose which is relatively inexpensive as to labor and material cost and which may be applied with the aid of apparatus now available for road or pavement work.

The above mentioned objects of the invention, as well as others, together with the advantages thereof will more fully appear as the specification proceeds.

In the drawing:

This exposes new through a concrete pavement to which my improved protecting coating has been applied.

Fig. 2 is a fragmentary vertical sectional view on an enlarged scale of a piece of concrete pavement, shown in Fig. 1, to which my improved protective coating has been applied.

Fig. 3 is a fragmentary plan view of a piece of concrete pavement shown in Fig. 2, to which my improved protecting coating has been applied, portions of the layers of the coating being shown as broken away for illustrative purposes.

Referring now in detail to that embodiment of the invention illustrated in the accompanying drawing, 5 indicates the crowned slab of a concrete pavement having a combined gutter and curb 6 along each side thereof. The slab may Fig. 1 is a transverse vertical sectional view be made from the usual approved mixture of sand, gravel or broken stone, cement and water in the desired proportions, the water combining with the cement to bind the whole mixture into a solid mass having the characteristics of strong artificial stone. When the concrete has set and hardened, it is porous so that moisture will penetrate thereinto.

In providing the improved protective coating embodying the present invention, it is desired that the exposed top surface of the pavement be free from dust, dirt and trash. Therefore, if the pavement to be protected is in a condition that requires cleaning, it may be cleaned by sweeping and flushing.

After the pavement surface has been cleaned, it is inspected for defects such as service cuts, low spots and cracks. It is desirable that the service cuts be repaired with suitable bituminous material, that the low spots be filled flush with patch material and that the cracks be filled with any approved crack filler, all in accordance with known concrete pavement repairing practices.

In providing the improved protective coating, tar is applied to the cleaned upper surface of the pavement. For practical reasons this application of tar is made by means of a motor distributor which generally includes a 1000 or 1500 gallon tank on a motor truck chassis. Such a tank is usually equipped with coils attached to a heating system for maintaining the tar at the proper temperature, say approximately A motor distributor of this kind usually includes a spray bar and means for pumping the tar from the tank to the spray bar for distribution over the surface of the pavement. The amount of tar applied per square yard of pavement surface is governed by the speed of the motor distributor;

Tar at the temperature mentioned is relatively fluid and will penerate voids and pores in the concrete pavement as thread-like roots shown in exaggerated form in Fig. 2 of the drawing and provide a good mechanical bond which holds the tar to the surface of said pavement.

Thereafter relatively small stone-like particles are applied to the tar and this follows closely upon the application of the tar. Preferably the stone-like particles are stone chips instead of pebbles and about 16 to pounds of the same are used per square yard of tarred surface. The stone chips should be of such hardness that they will not crush under rolling by a five ton roller, and should have the following sieve analysis:

Per cent Passing inch sieve '70 to 85 Passing A inch sieve 20 to Passing No. 8 sieve Not more than 3 These stone chips may be applied as follows: They may be hauled by motor trucks which are backed up onto the tarred surface and'discharged thereonto. An even distribution of said chips is secured by hand labor spreading. As soon as the stone chips are spread, the surface is rolled with a relatively heavy roller. In a relatively large area, the operation of tarring, the application of stone chips and the rolling can be carried on s multaneously on different parts of said area.

In the rolling operation the stone chips are 4 pressed into the tar so as to be substantially covered thereby, the rolling producing a relatively thin layer of tar and stone. In actual practice a layer of tar and stone chips thick well serves the purpose of a not heavily overloaded traffic street.

After the stone chips have been applied, they should cover the tar and therefore an excess may be applied so that the road may be opened to trafiic at this time, should traffic conditions make the same necessary. The reason for the excess is to prevent the tires of motor vehicles from coming into direct engagement with the tar. Under such conditions some of the stone chips will be picked up by the tires of the vehicles and others whipped into the gutters 6E. Such stone chips may be recovered for reuse later on In Fig. 2 the layer of tar and stone chips is indicated as a whole at i and the tar itself is indicated at 8. The thread-like roots of tar, which as before mentioned enter the pores of the concrete slab, in exaggerated form, are indicated at 5 and the stone chips are indicated at if].

After the tar has cooled and is properly cured, the loose excess stone chips are removed so that the first and bottom layer 1 of the protective coating is ready for the application of the second and finishing layer.

The second or finishing layer of the protective coating which is indicated at l l, includes asphalt which is applied in the same manner as the tar. As asphalt is more volatile than tar and so that it shal1 not catch afire, it is not heated to the temperature of the hot tar. Therefore the asphalt must be kept at a temperature, as for example, below 109 F. It is spread by means of a bituminous distributor and the proper temperature is maintained by a heater on the distributor. Preferably the asphalt employed for this purpose is a cut back asphalt. Specifications 130-3 and RC-4 as recommended by the Asphalt Institute well serve the purpose.

After the asphalt layer has been applied to the layer '1, chip stones similar to those employed in the tar are spread upon the asphalt and rolled thereinto by the roller before mentioned. In Fig. 2 the asphalt is indicated at l2 and the chip stones are indicated at it. Under the rolling action the layer I 1 receives, parts of the stone chips in one layer will be displaced to such an extent that they will enter the other layer to assist in forming a mechanical tie or bond between the two layers. Asphalt in a workable condition will not adhere to a concrete surface. In order for asphalt to be liquid enough to penetrate the pores of the concrete, it would not be viscous enough to hold stone chips on the surface of the concrete. Also to reach such a liquid state, asphalt would have to be heated to such a temperature that it would most likely catch afire.

Tar is'more liquid at its working temperature than asphalt and when hot, say at F., it is liquid enough to penetrate the pores in the concrete 5. When it is cold, it is viscous enough to hold the stone chips l0. Asphalt, however, when once applied to the layer 7, as above mentioned, will adhere tenaciously to the tar so that an intimate bond is present between the two layers that joins them together as a single duplex coating.

Tar has a tendency to dry out or oxidize in the presence of air to a greater extent than asphalt. Thus in the improved coating, the layer of asphalt over or upon the tar prevents air from coming in contact with the tar and thereby prevents it from becoming hard and brittle. In such a condition the shock of traffic would not only crack and break the tar, but it would break the bond between the tar and the concrete. The asphalt layer in this instance keeps the tar fluid and preserves the bond.

A protective coating made as described, not only Waterproofs the concrete slab of the pavement but it provides a new traflic wear-resisting surface for the pavement which is not slippery when wet as by an ordinary rain. A protective coating of th kind described is in no way affected by thawing materials and cannot be penetrated thereby. Such materials may be used when necessary without the danger of producing disintegration in the concrete of the pavement. As the improvedcoating efficiently protects the pavement against causes of disintegration, the period or life of the concrete pavement is materially increased.

While in describing the invention I have referred in detail to the materials used, as well as to the manner in which they are applied to a pavement, the same is to be considered only in the illustrative and not in the limiting sense, and therefore I do not wish to be limited thereto except as may be specifically set forth in the appended claims.

I claim as my invention:

1. In combination with the slab of a concrete pavement, a relatively thin protective surface coating therefor embodying a layer containing tar adhered directly to the upper surface of the slab through the action of the tar and which penetrates at least in part into the pores of the concrete of said slab, and a traffic wear-resisting surface layer disposed upon the first layer and containing asphalt bonded directly to the first layer, at least one of said layers embodying relatively small particles of stone or the like therein.

2. In combination with the slab of a concrete pavement, a relatively thin protective surface coating'therefor embodying a layer containing tar adhered directly to the upper surface of the slab through the action of the tar and which penetrates at least in part into the pores of the concrete of said slab, and a trafiic wear-resisting surface layer disposed upon the first layer and containing asphalt bonded directly to the first layer, both of said layers embodying relatively small particles of stone or the like therein.

3. In combination with the slab of a concrete pavement, a relatively thin protective surface coating therefor embodying therein a layer containing tar adhering directly to the upper surface of the slab through the action of the tar and which penetrates, at least in part, into the pores of the concrete of said slab, and a traffic wearresisting surface layer disposed upon the first layer and containing asphalt bonded directly to the first layer, at least the surface layer embodying stone chips therein.

4. The method of forming a protective surface coating upon the slab of a concrete pavement which consists in applying a relatively thin layer containing tar to the cleaned top surface of the slab and which tar is so fluid that some of the tar will penetrate into the pores of the concrete and adhere thereto, and then applying a second and relatively thin layer containing asphalt and relatively small particles of stone or the like to the top surface of the first layer under conditions which cause adhesion between said layers.

5. The method of forming a protective surface coating upon the slab of a concrete pavement which consists in applying tar to the cleaned top surface of a slab and which tar is so fluid that some of the tar will penetrate into the pores of the concrete and adhere thereto, applying small particles of stone to the tar So as to be embedded therein, to form the first and relatively thin layer of the coating, applying asphalt upon the first layer and then applying small particles of stone to the asphalt so as to be embedded therein and form the second and relatively thin layer of the coating and which layers are adhesively united through the affinity which tar and asphalt have for each other.

6. In combination with the slab of a concrete pavement, a protective coating therefor comprising a relatively thin layer of tar disposed upon and adhered directly to the upper surface of the slab and some of which tar penetrates into the pores of the concrete, a relatively thin, traffic wear-resisting surface layer of asphalt disposed upon and bonded directly to the layer of tar, and relatively small particles of stone pressed into each of said layers, certain of said particles of stone or the like disposed in the plane between said layers engaging the material of both layers and mechanically tying them together.

GEORGE H. SANDENBURGH. 

